Tuesday, March 13, 2012

Microsoft adds Mocking/Isolation support to Visual Studio 11

A lot has changed on the testing front inside Visual Studio 11.(If you want to know a good overview of all the changes: http://www.peterprovost.org/blog/post/Whats-New-in-Visual-Studio-11-Beta-Unit-Testing.aspx). One interesting feature I noticed in this long list of changes is the introduction of their own isolation framework:

The Visual Studio Fakes Framework

“Microsoft Fakes is an isolation framework for creating delegate-based test stubs and shims in .NET Framework applications. The Fakes framework can be used to shim any .NET method, including non-virtual and static methods in sealed types.”

Wow! As it also will support to fake both non-virtual and static methods, I can finally isolate some of the harder to (unit)test parts of the .NET ecosystem.

The Fakes framework helps developers create, maintain, and inject dummy implementations in their unit tests. It provides two ways to do this:

  • Stub types Stub types make it easy to test code that consumes interfaces or non-sealed classes with overridable methods. A stub is realized by a distinct type which is generated by the Fakes Framework. As a result, all stubs are strongly typed. 
  • Shim types Shim types allow detouring of hard-coded dependencies on static or non-overridable methods. A shim of type T can provide an alternative implementation for each non-abstract member of T. The Fakes Framework will redirect method calls to members of T to the alternative shim implementation.

Creating Fakes is as easy as right-clicking on one of your project references and choosing Add Fakes Assembly.

Read more about the Visual Studio Fakes Framework in the MSDN Documentation.

Remark: I didn’t add any sample code, as the syntax could still change.

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